1. Field of the Invention
The present invention relates to the activating flux for welding stainless steels. Particularly, the present invention relates to the activating flux including an active additive material selected from titanium dioxide (TiO2), chromium oxide (Cr2O3), silicon dioxide (SiO2), molybdenum disulphide (MoS2) and molybdenum trioxide (MoO3). More particularly, the present invention relates to the additive material of the activating flux for increasing a degree of the weld penetration capability and a degree of weldability of stainless steel material in arc welding techniques.
2. Description of the Related Art
Throughout the history of stainless steel, various techniques of conventional arc welding have been used. Generally, conventional arc welding includes Tungsten Inert Gas (TIG) Welding, Metal Inert Gas (MIG) Welding, Carbon Arc Welding (CAW), Submerged Arc Welding (SAW), Flux Cored Arc Welding (FCAW), etc.
By way of example, TIG welding, which uses an arc between a nonconsumable tungsten electrode and the workpieces to be welded under a shielding gas, is an extremely important arc welding process. In the arc welding process, a welding torch supplies an inert gas as well as a protective gas on a predetermined position of the stainless steel for the welding operation. The inert gas can prevent oxidation on the electrode, weld pool and adjacent heat-affected zone (HAZ) so as to cool and solidify a weld bead. However, when processing full penetration on the stainless steel welds, a number of limitations and drawbacks exist for TIG welding. The primary problem with such TIG welding is that the welds are susceptible to problems of insufficient penetration depth, varied penetration depth and broad, shallow weld pool. This results from a slight change of alloy elements of the workpiece. Accordingly, there is a need for increasing penetration in TIG welds so as to increase a degree of full penetration welds.
In view of the potential problem, various approaches have been used to enhance the TIG welding characteristics. Turning now to FIGS. 1A, 1B and 1C, various views of pre-processing a workpiece for conventional TIG welding and welding two processed workpieces together are shown. For eliminating the problem of broad, shallow weld pool, a milling cutter 2 is used to cut a side wall 11 of a workpiece 1 so as to form an inclined surface 12 on the side wall 11. The inclined surface 12 of the workpiece 1 abuts against an inclined surface 12′ of another workpiece 1′ to define a V-groove therebetween for forming a butt joint. In the welding operation, a welding torch 3 and a welding rod 100 are used to execute the TIG welding process between the two workpieces 1, 1′ to form welds 13. Although such an arrangement of the inclined surface 12 is successful in increasing depth of the welds 13, forming the inclined surface 12 sophisticates the manufacturing process and increases manufacturing cost and time.
Another conventional welding flux disclosed in U.S. Patent Publication No. 2005/0199317, entitled “Welding Flux for Use in Arc-Welding of Stainless Steels, Method of Welding Stainless Steel Members Using the Welding Flux,” includes a base material of manganese peroxide MoO2. Furthermore, one additive material of zinc oxide (ZnO), silicon dioxide (SiO2), chromium oxide (CrO2), titanium dioxide (TiO2), molybdenum dioxide (MoO2) and ferric oxide (Fe2O3) may also be added to the base material. The base material occupies more than 70 wt % of the total flux, while the additive materials occupy less than 30 wt % of the total flux.
Turning now to FIGS. 2A and 2B, perspective and side elevational views of two workpieces welded by using flux disclosed in U.S. Patent Publication No. 2005/0199317 are shown. A welding flux 4 is made from a flux paste disclosed in U.S. Patent Publication No. 2005/0199317. A brush 40 is utilized to smear the flux 4 around an abutting portion between the two workpieces 1, 1′ in preparing an arc welding process on the two workpieces 1, 1′ such that the flux 4 is coated above a portion of a boundary line located between the two abutting side walls 11 of the two workpieces 1, 1′. After the welding process, the welds 13 are formed between the two abutting side walls 11, 11′ of the two workpieces 1, 1′. Advantageously, spatter or slag rarely occurs around the welds 13 in the welding operation due to the use of the flux 4. A top surface of the welds 13 is nearly identical with top surfaces of other areas of the workpieces 1, 1′. It is apparent from FIG. 2B that the welds 13 formed between the two workpieces 1, 1′ is successful in narrowing its width and is formed in full penetration welds.
Turning now to FIGS. 3A and 3B, enlarged, side elevational views of liquid-state metal flows in a weld pool located between two workpieces are shown. The primary approach for improving the welding quality is that the base material of MoO2 and the additive material are added to the flux 4. Accordingly, the flux 4 applied to the workpieces 1, 1′ can change a gradient of surface tension of the liquid-state metal on the surface of a weld pool 10 in the welding process and can influence directions of liquid-state metal flows in the weld pool 10. Changes of the gradient of surface tension of the liquid-state metal involve the temperature coefficient of the weld pool 10. Furthermore, the temperature coefficient of surface tension of the weld pool 10 depends upon whether an active element in the liquid-state metal is contained.
With continued reference to FIG. 3A, the flux 4 or the weld pool 10 does not contain an active element or a relatively inactive element(s). In this welding process, as the arc temperature supplied from the welding torch 3 increases, the surface tension of the weld pool 10 decreases. The decrease in the surface tension causes the liquid metal to generate outward liquid metal flows (i.e. outward surface tension flows) from a center portion of the weld pool 10. Disadvantageously, such outward liquid metal flows results result in an unwanted broad, shallow configuration of the welding bead.
With further reference to FIG. 3B, the flux 4 or the weld pool 10 contains relatively active elements. In this welding process, as the arc temperature supplied from the welding torch 3 increases, the surface tension of the weld pool 10 also increases. An increase of the surface tension causes the liquid metal to generate inward liquid metal flows (i.e. inward surface tension flows) from peripheral portions to a center portion of the weld pool 10. Advantageously, such inward liquid metal flows result in a preferred narrow and deep configuration of the welds.
It is apparent from FIG. 3B that the additives of active elements added to the mixture of the flux 4 are successful in forming a preferred narrow and deep configuration of the welds. However, the conventional flux 4 contains a great amount of the base material of MoO2 which is an inactive material for the arc welding. Furthermore, there is a need of smearing the flux 4 on side walls 11, 11′ of the workpieces 1, 1′ such that an additional smearing step may sophisticate the entire arc welding process. In addition, an additional pre-fabricating procedure for the flux 4 may further sophisticate the entire arc welding process. Accordingly, there is a need of modifying the flux 4 so as to improve the welding quality of stainless steels.
As is described in greater detail below, the present invention provides an activating flux for welding stainless steels. The activating flux includes active additive materials of TiO2, Cr2O3, SiO2, MoS2 and MoO3 which can increase a deep degree of fill penetration in stainless steel welds and enhance a degree of weldability of the arc welding operation. In addition, the active additive materials can enhance a degree of uniformity, mechanical strength, and impact toughness of the weldment. Accordingly, the flux of the present invention can improve the welding quality of stainless steels in such a way as to mitigate and overcome the above problem. Advantageously, the activating flux is successful in simplifying the arc welding process and increasing the efficiency of arc welding.